Vietnamese citrus interplanted with guava had higher mite populations and higher incidences of canker and scab. Guava poses additional concerns to citrus growers and researchers. IFAS — Be cautious By T.M. Spann, M.E. Rogers and L.W. Timmer about guava

site without guava had infection rates of 30 to 40 percent. Immature fruit and leaves of guava. The results also a direct threat to Florida citrus pro - showed that citrus duction, Caribfly management is nec - trees planted with essary to export fruit to some guava had very low domestic and foreign markets as man - populations of dated by the Caribbean Fruit Fly Pro - adults and nymphs tocol of the Florida Department of of the Asian citrus Agriculture and Consumer Services. psyllid ( Diaphorina These rules include the creation of citri Kuwayama — fly-free zones around groves produc - the insect vector of ing fruit for export. One of the re - greening) per tree quirements for creating a fly-free compared with zone is that the designated grove area those not planted and a buffer zone be free of preferred with guava. The hosts such as guava, Surinam cherry, guava trees were and other soft-fruited species. Guavas and newly set fruit of guava. thought to have ei - In addition to serving as a host of ecently there has been considerable ther acted as a natural repellent of the Caribfly, the IFAS Assessment of the publicity about the use of guava psyllid or were toxic to the insect. The Status of Non-Native Plants in Flor- R(Psidium guajava L. ) trees to fight larger size of the guava trees as op - ida’s Natural Areas has concluded that huanglongbing (HLB, citrus greening) posed to the newly planted citrus may guava is an invasive species and it is in Florida, but IFAS recommends cau - also have made it difficult for pests to NOT RECOMMENDED for planting tion regarding this proposal. The infor - locate the citrus hosts. by IFAS. Furthermore, the Florida Ex - mation that has stirred this discussion While these data initially look in - otic Pest Plant Council lists guava as a comes from observations reported from teresting, caution is advised. Despite Category I invasive plant, meaning that some Vietnamese citrus growers who interplanting with guava, Vietnamese it is “altering native plant communities for the past 15 to 20 years have inter - farmers who have maintained such in - by displacing native species, changing planted citrus with guava. These grow - terplantings for more than 15 years re - community structures or ecological ers believe that such interplanting port that psyllids are still present in functions, or hybridizing with natives.” might delay significant losses due to these groves and management of the The current research in Vietnam rep - greening by either repelling psyllids or psyllid is still needed. Therefore, these resents only a single unreplicated test hindering the ability of psyllids to lo - farmers routinely monitor new flushes with very small trees and it remains to cate citrus plants. The effects of guava for the presence of psyllids and hand be seen whether similar results would on psyllid populations and HLB inci - remove any flush on which psyllids be obtained under other conditions or dence is being further investigated by are observed. Petroleum oil sprays are as the trees matured. In addition, inter - Vietnamese and Australian researchers, also routinely used by the Vietnamese planting of any crop with citrus pres - and the USDA is conducting field stud - to help reduce psyllid populations ents many problems in terms of ies with guava trees in South Florida. when new flush is anticipated. harvesting practices, equipment move - In an unreplicated trial in the Cai MITES, CANKER, ment, potential competition and shad - Be region of the Mekong Delta of SCAB, CARIBFLY ... ing, and may require modification of Vietnam, two blocks of trees were irrigation and fertilization practices. planted several kilometers apart. One The investigators of the above REDUCED YIELD block was planted as a solid block of mentioned study indicated that the citrus trees and in the other, citrus was citrus trees interplanted with guava Planting guava in a 1:1 ratio with interplanted with guava in a 1:1 ratio. had higher mite populations and citrus would reduce yield by 50 per - After a period of one year, no greening higher incidences of canker and scab. cent due to the loss of acreage, al - was detected in the citrus trees planted Additionally, guava is a preferred though other planting arrangements in the presence of guava at one site host of Caribbean fruit fly, Anas - that are less “invasive” are possible. whereas those planted at the second trepha suspense , in Florida. While not The guava trees would also produce

CITRUS INDUSTRY • March 2007 copious amounts of fruit for which observations on guava may yield psyllids as well. there is currently only a small market. some new data for control of Asian However, guava is an invasive, At the same time, grove management citrus psyllids. Future research to de - exotic species, and until more evi - costs would probably remain the same termine if there are chemical com - dence supports the use of guava to re - or possibly increase due to new pest pounds in guava that may affect duce psyllid populations and greening and disease pressures. Guava is not psyllids could help us better under - spread, IFAS is not recommending cold tolerant and may not survive in stand psyllid behavior and whether or interplanting citrus with guava. the northern citrus areas. Even if it not such compounds can be formu - L. W. Timmer is a professor; T. M. proved highly effective, cultural prac - lated for use in psyllid management Spann and M. E. Rogers are assistant pro - tices would have to be greatly modi - programs. Also, other Myrtaceous fessors; all are at the University of fied to accommodate the changes. species related to guava might be Florida’s Citrus Research and Education Despite the negative aspects, these studied as to their potential effects on Center in Lake Alfred.

CITRUS INDUSTRY • March 2007